Plants are continuously exposed to a vast multiplicity of stressful factors, both of biotic or abiotic nature, that negatively affect their development, yield, and reproductive success. To withstand environmental changes plants have developed complex and sophisticated strategies, among which sensitive detection systems and complex signal transduction pathways. These intricate mechanisms ultimately lead to transcriptional induction of genes encoding proteins enabling adaptation to environmental challenge. Epigenetic modifications, among these DNA methylation, represent potentially robust mechanisms contributing to gene expression regulation during periods of environmental stress. The presence of enzymes involved in DNA demethylation, namely Repressor of Silencing 1, DEMETR, and DEMETR-like, makes modulation of DNA methylation highly ductile in plants. Indeed, cytosine methylation and demethylation within the promoter sequence have been shown to cause gene downregulation and upregulation, respectively, in response to different environmental stress. Due to the sessile nature of plants, this epigenetic mechanism is crucial to permit a suitable plant reaction to stress, resulting in short-term acclimation. However, plants should also be able to reset the stress-induced epigenetic alterations in order to restart normal growth when favorable environmental conditions come back.

In this chapter, dynamics and biologic significance of changes in DNA methylation patterns in plant responses to changing environment will be discussed.